The use of an electric motor to rotate a fan blade to create an airflow has long been known in the art. Unfortunately, such fans produce substantial noise, and can present a hazard to children who may be tempted to poke a finger or a pencil into the moving fan blade. Although such fans can produce substantial airflow (e.g., 1,000 ft3/minute or more), substantial electrical power is required to operate the motor, and essentially no conditioning of the flowing air occurs.
It is known to provide such fans with a HEPA-compliant filter element to remove particulate matter larger than perhaps 0.3 μm. Unfortunately, the resistance to airflow presented by the filter element may require doubling the electric motor size to maintain a desired level of airflow. Further, HEPA-compliant filter elements are expensive, and can represent a substantial portion of the sale price of a HEPA-compliant filter-fan unit. While such filter-fan units can condition the air by removing large particles, particulate matter small enough to pass through the filter element is not removed, including bacteria, for example.
It is also known in the art to produce an airflow using electro-kinetic technique, by which electrical power is converted into a flow of air without mechanically moving components. One such system is described in U.S. Pat. No. 4,789,801 to Lee (1988), which patent is incorporated herein by reference. An array of first (“emitter”) electrodes or conductive surfaces are spaced-apart symmetrically from an array of second (“collector”) electrodes or conductive surfaces. The positive terminal of a generator such as, for example, pulse generator that outputs a train of high voltage pulses (e.g., 0 to perhaps +5 KV) is coupled to the first array, and the negative pulse generator terminal is coupled to the second array in this example. It is to be understood that the arrays depicted include multiple electrodes, but that an array can include or be replaced by a single electrode.
The high voltage pulses ionize the air between the arrays, and create an airflow from the first array toward the second array, without requiring any moving parts. Particulate matter in the air is entrained within the airflow and also moves towards the second electrodes. Much of the particulate matter is electrostatically attracted to the surfaces of the second electrodes, where it remains, thus conditioning the flow of air exiting system. Further, the high voltage field present between the electrode arrays can release ozone into the ambient environment, which can eliminate odors that are entrained in the airflow.
While the electrostatic techniques disclosed by the '801 patent are advantageous over conventional electric fan-filter units, further increased air transport-conditioning efficiency would be advantageous.